This invention relates to a power transmission unit for motor vehicles, and more specifically to a lubrication apparatus for use in the power transmission unit which can provide good lubrication of bearings supporting an elongated rotary shaft within a casing of the power transmission unit even when the vehicle body is in an inclined state.
There is known as a related art a lubrication apparatus used in a final drive and differential unit for motor vehicles, of such a type that includes a casing elongated in a fore-and-aft direction of the motor vehicle and receiving lubricating fluid, a differential case arranged at a rear end of the casing, a differential gear unit rotatably disposed within the differential case, a drive gear mounted to the differential case, and a drive pinion shaft that is formed with a drive pinion meshing with the drive gear. The drive pinion shaft is elongated forward to be connected with a front-wheel side trans-axle via a propeller shaft. The drive pinion shaft is rotatably supported by a pair of axially spaced tapered roller bearings at a rear portion thereof near the differential case and by a ball bearing of a sealing type at a front portion thereof. The ball bearing of the sealing type is filled with grease. With this arrangement, when the motor vehicle is in a normal horizontal position, the roller bearings and the ball bearing are immersed in the lubricating fluid to be sufficiently lubricated. On the other hand, when the motor vehicle runs on a rapid ascent, the ball bearing lifts up from the level of the lubricating fluid whereby positive lubrication of the ball bearing is not achieved. This is the reason why the ball bearing of the sealing type is used at the front portion of the drive pinion shaft. Meanwhile, when the motor vehicle runs on a rapid descent, the roller bearings at the rear portion of the drive pinion shaft are still immersed in the lubricating fluid owing to a volumetric difference between a front end portion of the casing and a rear end portion thereof.